Substorm Auroral Dynamics Reproduced by Advanced Global Magnetosphere−Ionosphere (M–I) Coupling Simulation

Tanaka, Takashi

doi:10.1002/9781118978719.ch13

Cited by 46 publications

(151 citation statements)

References 30 publications

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“…This is pointed out by Birn and Hesse (). This is near‐Earth dynamo, which is in close relation with the onset FAC (Ebihara & Tanaka, , ; Tanaka, ).…”

Section: Resultsmentioning

confidence: 56%

“…It is a general presumption in these models that the onset FACs come from the equatorial plane along a field line. On the contrary, it is shown that the current line deviates from the magnetic field line at off‐equator (Tanaka, ) and that the vortex being responsible for the onset FAC appears at off‐equatorial low‐altitude region (Ebihara & Tanaka, ).…”

Section: Introductionmentioning

confidence: 99%

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Energy Flow Exciting Field‐Aligned Current at Substorm Expansion Onset

Ebihara

Tanaka

2017

JGR Space Physics

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At substorm expansion onset, upward field‐aligned currents (FACs) increase abruptly, and a large amount of electromagnetic energy starts to consume in the polar ionosphere. A question arises as to where the energy comes from. Based on the results obtained by the global magnetohydrodynamics simulation, we present energy flow and energy conversion associated with the upward FACs that manifest the onset. Our simulations show that the cusp/mantle region transmits electromagnetic energy to almost the entire region of the magnetosphere when the interplanetary magnetic field is southward. Integral curve of the Poynting flux shows a spiral moving toward the ionosphere, probably suggesting the pathway of electromagnetic energy from the cusp/mantle dynamo to the ionosphere. The near‐Earth reconnection initiates three‐dimensional redistribution of the magnetosphere. Flow shear in the near‐Earth region results in the generation of the near‐Earth dynamo and the onset FACs. The onset FACs are responsible to transport the electromagnetic energy toward the Earth. In the near‐Earth region, the electromagnetic energy coming from the cusp/mantle dynamo is converted to the kinetic energy (known as bursty bulk flow) and the thermal energy (associated with high‐pressure region in the inner magnetosphere). Then, they are converted to the electromagnetic energy associated with the onset FACs. A part of electromagnetic energy is stored in the lobe region during the growth phase. The release of the stored energy, together with the continuously supplied energy from the cusp/mantle dynamo, contributes to the energy supply to the ionosphere during the expansion phase.

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“…This is pointed out by Birn and Hesse (). This is near‐Earth dynamo, which is in close relation with the onset FAC (Ebihara & Tanaka, , ; Tanaka, ).…”

Section: Resultsmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Energy Flow Exciting Field‐Aligned Current at Substorm Expansion Onset

Ebihara

Tanaka

2017

JGR Space Physics

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“…Recently, it has been presented that the finer the spatial resolution of the global magnetohydrodynamic (MHD) simulations, which consider the effects of the magnetosphere‐ionosphere (M‐I) coupling, the more realistic the features of the auroral or polar substorms that can be reproduced [ Tanaka et al ., ; Ebihara et al ., ; Tanaka , , hereinafter referred to as Paper 1; Ebihara and Tanaka , , Paper 2; Ebihara and Tanaka , , Paper 3]. In these precise simulations, ionospheric elements of substorms, such as the sudden decrease in the Auroral Lower ( AL ) index, the quiet arc, the dipolarization front, the initial brightening, the westward traveling surge (WTS), the double oval, and the overshielding, are reproduced.…”

Section: Introductionmentioning

confidence: 99%

Substorm simulation: Quiet and N‐S arcs preceding auroral breakup

Ebihara

Tanaka

2016

JGR Space Physics

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Auroral breakup at the onset of substorm expansion is sometimes preceded by auroral forms known as quiet arcs and N‐S arcs. Observations have shown that both the auroral forms tend to move equatorward, and the initial brightening takes place in or near one of the quiet arcs. The auroral forms attract great attention, but generation of auroral forms and their association with the initial brightening are poorly understood. Recent global magnetohydrodynamic simulations are capable of producing upward field‐aligned currents (FACs) that resemble the auroral forms in both shape and temporal evolution. Based on the simulation results, we propose the following scenarios: (1) When the convection electric field is weak (northward interplanetary magnetic field (IMF)), the high‐pressure region is elongated from the plasma sheet toward higher latitudes and is structured by a coupling between the magnetosphere and the ionosphere (interchange‐like instabilities). (2) When the convection electric field is strong (southward IMF), the structured high‐pressure region moves equatorward (toward the plasma sheet). Upward currents are generated around it, which can be observed as arcs in the ionosphere. The upward current can be tentatively intensified in the course of the equatorward movement before the formation of a near‐Earth neutral line (NENL). (3) The NENL releases magnetic tension and results in the enhancement of plasma pressure at off‐equator in the near‐Earth region. Sudden formation of the off‐equatorial high‐pressure region generates the onset current system that manifests initial brightening. Our scenario can explain the observational fact that poleward arcs remained undisturbed at the onset.

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“…REPPU employs a grid system based on triangular prisms. They include, for example, auroral electrojets (Ebihara et al, 2019;Takashi Tanaka, 2015) Joule dissipation rates (Ebihara et al, 2019), a westward traveling surge (Ebihara & Tanaka, 2015a;Tanaka, 2015), and counter electrojet at the magnetic equator (Ebihara et al, 2014), earthward fast flow in the plasma sheet (Tanaka et al, 2017), dipolarization in the near-Earth magnetosphere (Tanaka et al, 2017), generation of fieldaligned currents directly related to substorm expansion (Ebihara & Tanaka, 2015a, 2015bTanaka, 2015). We further divide each pentagon into five triangles and obtain 60 triangles in total (Level 1).…”

Section: Global Mhd Simulationmentioning

confidence: 99%

Nonlinear Wave Growth Analysis of Whistler‐Mode Chorus Generation Regions Based on Coupled MHD and Advection Simulation of the Inner Magnetosphere

et al. 2020

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We show the regions where nonlinear growth of whistler-mode chorus waves is preferred to occur in the inner magnetosphere. A global magnetohydrodynamics (MHD) simulation was used to obtain large-scale electric and magnetic fields under the southward interplanetary magnetic field condition. With the electric and magnetic fields obtained by the MHD simulation, we ran a comprehensive inner magnetosphere-ionosphere model to solve the evolution of phase space density of electrons. Hot electrons originating from the tail region drift sunward and penetrate deep into the inner region due to a combination of convection and substorm-associated electric fields. Cold electrons also drift sunward, resulting in a contraction of the plasmasphere. We obtained the following results. (1) The whistler waves can first grow due to the linear mechanism (pitch angle anisotropy) in the premidnight-prenoon region outside the plasmapause, followed by rapid, nonlinear mechanism accompanied with rising-tone chorus elements. (2) When the solar wind speed is high, the whistler waves grow more efficiently due to linear and nonlinear mechanisms over a wider area because of deep penetration of hot electrons and the large contraction of the plasmasphere. This is consistent with the observation that the outer belt electrons increase for the fast solar wind.(3) For slow solar wind, the linear growth is mostly suppressed, but the nonlinear growth can still take place when external seed waves are present. This may explain the persistence of dawn chorus and largeamplitude chorus waves that are often observed in the premidnight-postdawn region in relatively weak geomagnetic activities.

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Substorm Auroral Dynamics Reproduced by Advanced Global Magnetosphere−Ionosphere (M–I) Coupling Simulation

Cited by 46 publications

References 30 publications

Energy Flow Exciting Field‐Aligned Current at Substorm Expansion Onset

Energy Flow Exciting Field‐Aligned Current at Substorm Expansion Onset

Substorm simulation: Quiet and N‐S arcs preceding auroral breakup

Nonlinear Wave Growth Analysis of Whistler‐Mode Chorus Generation Regions Based on Coupled MHD and Advection Simulation of the Inner Magnetosphere

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